It is conventional to mix and mill aggregate materials in the preparation of forming a casting such as concrete or for the forming of bricks, blocks and other cast items. Machines for performing such mixing and milling, sometimes referred to as pug mills, are illustrated in U.S. Pat. No. 2,187,897 to Bollard issued Jan. 23, 1940, U.S. Pat. No. 2,570,042 to West issued Oct. 2, 1951 and U.S. Pat. No. 4,775,239 to Martinek et al. issued Oct. 4, 1988.
Bollard, West and Martinek are directed primarily to replaceable blades bolted at the ends of mounting shanks. The blades are subjected to substantial abrasion and wear and it is thus necessary for the blades to be replaceable. However, the shanks to which the blades are mounted and even the bolts which secure the blades to the shanks are also subjected to substantial abrasion and wear. Accordingly, in conventional pug mills it is frequently necessary to replace the mounting shanks as well which presents a substantial disadvantage and cost. The above patented designs provide for relatively easily replaceable blades, however, replacement of the shanks may cause substantial down time for the mixing apparatus as well as additional costs for replacement items.
A different prior art arrangement for securing the blade to the shaft is illustrated in FIG. 3 in the attached drawing. The prior art blade 21 is formed of a heavy cast material which is carried on the rotating shaft by a shank 22. The shank 22 is secured to the shaft and extends generally radially from the shaft. The blade 21 is cast with a series of threaded bolt portions 23 extending from the rearward portion of the blade so as to be inserted through corresponding holes in the shank 22. Nuts 24 secure the bolt portions and thereby hold the blade 21 firmly to the shank 22. However, this prior art arrangement has several disadvantages. As with the references discussed above, the shank 22 is exposed to the abrasive effects of the aggregate material which tends to wear out the shank 22 and the nuts 24. Further, replacement of the blade 21 is a difficult and laborious task because of the problem of aligning the bolts with the holes in the shank which is made further difficult by substantial weight of the blade 21 and the confined working area.
Accordingly it is an object of the present invention to provide an apparatus for mixing aggregate materials which avoids the drawbacks of the prior art as noted above and provides longer lasting life for the shank.
It is a more particular object of the present invention to provide an apparatus for mixing aggregate materials with a longer lasting life for the shank and for the bolt securing the blade to the shank.
It is a further object of the present invention to provide an apparatus for mixing aggregate materials with an improved blade design which facilitates easier replacement of the blade.